1. Field of the Invention
The invention relates to processing of information signals.
2. Background Information
A composite signal has two or more components whose values are related in time. Such signals are frequently encountered in communications applications. In an audio application, for example, a stereo signal may have a first component whose value over time defines the left channel of the signal and a second component whose value over time defines the right channel of the signal and is related in time to that of the first component.
Similarly, in a radio-frequency application, a composite signal that carries a baseband signal for modulation onto a carrier may have two components: a first component whose values over time define a data stream to be modulated onto the I (in-phase) component of the carrier, and a second component whose values over time define a data stream to be modulated onto the Q (quadrature) component of the carrier and are related in time to those of the first component.
In these and other instances, the components of a composite signal may describe a number of time-varying processes that are related in time, or two or more of the components may describe different aspects of a single time-varying process. In either case, a time relation between the components of a composite signal conveys essential information. For example, if the time relation between the components of a stereo signal is lost (e.g. because one component is delayed during transmission by an unknown period relative to the other component), the signal will not be reproduced correctly.
Likewise, a time relation between the components of a composite signal in a radio-frequency application may convey essential information. In one such example, the co-pending U.S. patent application Ser. No. 09/452,045, entitled “METHOD AND APPARATUS FOR ROTATING THE PHASE OF A COMPLEX PSK SIGNAL,” filed Nov. 30, 1999 and assigned to the assignee of the present application, describes methods of combining the I and Q components to perform an operation such as rotating the phase angle of a complex signal (e.g. to effectively exploit the dynamic range of a subsequent processing stage). If one of the components is delayed relative to the other, the phase angle will be altered and the desired effect may be lost. In transferring a composite signal between stages of a processing system, therefore, it is important to preserve the time relation between the components.
In many applications, it is desirable to implement successive stages of a processing path using physically distinct assemblies, printed circuit boards, chips, or components, or physically distinct regions of such units. In such cases, it may become necessary or desirable to transfer a composite signal between stages over a signal path (e.g. pins on a chip, a circuit bus, or a frequency band of a wireless transmission channel) that can only accommodate the values of fewer than all of the components at once. For example, it may be necessary or desirable to limit the number of terminal connections (e.g. pins) on a chip package, to limit the number of traces in a circuit bus, or to limit a number of frequency channels such that only a reduced signal path is available to carry a composite signal. It is desirable to transfer a composite signal over a reduced signal path without affecting the time relation between the signal's components.